In the dark, distant years of independent aquarium systems, when days were long, backs were sore and arms appreciably stronger, aquatics hobbyists, retailers, wholesalers et al. were oft heard making strong slogans such as, "Water change day!", "Top off that row!" "Where's that pickle bucket?"
As time went by, craniums got larger, arms got smaller and economic evolution prevailed. First it was the collector/breeders and trans-shippers that got the new religion; leading to the livestock wholesale distributors; blending to the savvy retailers to the advanced hobbyist. They all got the new religion: centralized filtration!
The advantages of "batch-processing" your water through collective reservoir sumps, filters and make-up have been well elucidated (Fenner & Lawracy, 4/87 PSM). The upside is less and easier maintenance, better water quality, lower mortality & morbidity, increased carrying capacity with larger margins for error. In other words, more fun, time and money!
The downside is more planning and up-front cost. I assure you, this is time and money very well invested. So much more labor will be otherwise expended and losses accumulated; not to mention unsightly buckets, hoses, sinks, splashes and related liability... By all means; if you're building out or refurbishing a part or all your aquatic holding system(s), centralize!
Some large volume wholesale distributors utilize once-through systems, where water is treated physically, chemically and possibly biologically; pumped to the holding facility and over-flowed to waste. This technique is not appropriate for most retailers who are better off recirculating, mixing system water.
How it Works:
Each tank or tub on a system is drilled and fitted with an overflow through the back or a bottom standpipe. Acrylic aquaria are easily drilled with a hole saw; glass tanks should be drilled before assembly by their manufacturer.
Overflow water gravity feeds via pipe to the reservoir sumps, out of the public view. Here the water is heated, filtered and sterilized; using some combination of fluidized bed (wet-dry), sand, diatomaceous-earth, cartridge filtration to remove particulates; chemical filtrants such as carbon, peat and zeolite; and physical filters like ultraviolet sterilization ozone, protein skimmers to reduce organics. There are many companies offering these products and design services (see p.282 of PSM's Buying Guide & Directory, Special Products and Services under Consultants)
We use at least four separate sump systems in our stores:
1) Coldwater; for Koi, Goldfish and cooler-water plants and invertebrates.
2) Freshwater Tropical; for fishes, inverts, and plants.
3) Marine Fishes; excepting some sensitive species like Clownfishes and Seahorses.
4) Marine Invertebrates, algae, live-rock and sensitive fishes.
Some stores have further divided systems with specialized brackish water, softer-acidic, warmer and harder-more-alkaline sump systems.
We still like to vacuum our gravel beds once a week. This is done after-hours with an "exploded-end" commercial vacuum fitted to a good 3/4 inch hose to waste. Refilling of tanks is accomplished through an auto-fill fitted into the freshwater sumps and new saltwater mix made up in the marine sumps.
Water is returned to the separate aquaria via centrifugal pumping and plastic pipe and valves. Additionally we use air driven under-gravel filtration and aerators in many of our aquaria for back-up.
The best time to install centralized filtering is when first building out your location; although this great leap forward can be accomplished effectively when remodeling/upgrading your set-up. Whenever you decide; do it! The savings in reduced livestock and personnel stress is considerable. The difference will show in a less-sore back, cleaner and safer store and larger profits.